Remote sensing radar has been under development for the past several decades. It has provided a means for long-range continuous all-weather day/night observational capabilities that were not previously available. We now have the ability to perform long-distance ranging, observe large-scale weather patterns, construct digital elevation maps, measure significant changes in the earth's surface, map mineral distributions, detect moving targets and even construct images using measured radar echoes and sophisticated modern processing.
Space Time Adaptive Processing (STAP) is a well-known method used to process spatio-temporal data to detect moving targets by employing a whitening operation followed by matched filtering in the spatio-temporal domian (J. Ward, Space-time adaptive processing for airborne radar. MIT Lincoln Laboratory, Technical Report 1015, December 1994; J. R. Guerci, Space-Time Adaptive Processing for Radar. Artech House; S. U. Pillai, K. Y. Li, and B. Himed, Space Based Radar: Theory & Applications. McGraw Hill Professional, December 2007.). SAR imaging was invented in the 1950s and has since been under continuous development. It is capable of imaging large swathes of terrain and all manners of objects visible to instruments operating in the RF spectrum. Moving target indication (MTI) such as air MTI (AMTI) and ground MTI (GMTI) are heavily used in both the military and civilian sectors for monitoring air and ground traffic. MTI radars are widely used for discrete surveillance and monitoring of sensitive areas. ATI is a well-known technique based on SAR images obtained from two phase centers separated by some distance in the along-track dimension (P. A. Rosen, Principles and Theory of Radar Interferometry, Tutorial for IGARSS, JPL Sep. 19, 2004). The advantage provided by ATI over SAR imaging alone is that by correlating the images from two different phase centers, the clutter scene (stationary background) is cancelled out and only moving targets are emphasized. ATI along with STAP has been used for estimating the velocities of both endoclutter and exoclutter targets. Slow-moving targets that are within the Doppler ridge generated by the platform are referred to as being in endoclutter while targets that are external to the Doppler ridge are referred to as being in exoclutter. ATI has an advantage over STAP when estimating the velocity of targets in endoclutter whereas STAP is more efficient at detecting targets in exoclutter.